1. Field of the Invention
The present invention relates to a road friction coefficients estimating apparatus for a vehicle for estimating friction coefficients on road surfaces and more particularly to a road friction coefficients estimating apparatus capable of properly estimating friction coefficients on road surfaces according to traveling conditions.
2. Discussion of Prior Arts
In recent years, numerous vehicle control technologies such as traction control technologies, braking force control technologies, torque distribution control technologies and the like, have been proposed and some of these control technologies have been realized in actual automobile markets. Many of these control technologies use friction coefficients on road surfaces (hereinafter, referred to as xe2x80x9croad friction coefficientxe2x80x9d) for calculation or correction of control parameters. Accordingly, in order to execute the control properly, it is necessary to estimate accurate road friction coefficients.
Several technologies in which road friction coefficients are estimated based on vehicle motion parameters such as lateral acceleration, yaw rate have been proposed. For example, the applicant of the present invention proposes a technology in which road friction coefficients are estimated based on the comparison of an actual yaw rate estimated from an observer with a high friction coefficient road reference yaw rate calculated using a vehicle motion model on a high friction coefficient road surface and with a low friction coefficient road reference yaw rate calculated using a vehicle motion model on a low friction coefficient road surface respectively in Japanese Patent Application No. Toku-Gan-Hei 11-217508.
However, a road friction coefficient estimating apparatus in which a road friction coefficient is estimated based on conditions of vehicle motion has a problem that especially when the vehicle travels at high speeds, because the change of yaw rate, lateral acceleration and steering angles is very small even under the large effect of road friction coefficients, it is extremely difficult to accurately estimate road friction coefficients by detecting this small change.
It is an object of the present invention to provide a road friction coefficients estimating apparatus capable of properly establishing road friction coefficients of a vehicle traveling at high speeds.
To achieve the object, the road friction coefficient estimating apparatus for a vehicle comprises a motion parameter detecting means for detecting motion parameters of the vehicle, a traveling circumstance recognition means for detecting traveling circumstances and for outputting a recognition signal indicative of a road surface covered with snow, a low friction coefficient road traveling condition detecting means for detecting a traveling condition indicative of a traveling on a road surface having low friction coefficient, a low side road friction coefficient estimating means for estimating a low side road friction coefficient according to an adaptive control theory and to a vehicle motion model based on the motion parameters and the traveling condition indicative of a traveling on a road surface having low friction coefficient and a road friction coefficient estimating means for estimating a road friction coefficient based on the motion parameters by comparing an actual yaw rate with a high friction coefficient road reference yaw rate and a low friction coefficient road reference yaw rate.
Further, the road friction coefficient estimating means renders the road friction coefficient first estimated by the road friction coefficient estimating means itself gradually close to a road friction coefficient established beforehand of an asphalted road surface when the vehicle travels at high speeds. Further, the road friction coefficient estimating means renders the road friction coefficient first estimated by the road friction coefficient estimating means itself gradually close to the low side road friction coefficient when the recognition signal is inputted. Further, the road friction coefficient estimating means renders the road friction coefficient first estimated by the road friction coefficient estimating means itself gradually close to the low side road friction coefficient when the vehicle travels at high speeds and when the recognition signal is inputted.